Block

A block in a blockchain is a data structure that records transactions occurring within a specific period, forming the foundational unit of a blockchain network. Each block contains transaction details, a timestamp, and a unique cryptographic hash, which securely links it to the previous block in the chain. This sequence of interconnected blocks ensures data integrity, immutability, and transparency within decentralized networks. 

Blocks are added to the blockchain through consensus mechanisms like Proof of Work (PoW) or Proof of Stake (PoS), ensuring that only valid transactions are confirmed. Once a block is added, its data becomes permanent and cannot be altered without compromising the entire blockchain, making blockchain technology highly secure and resistant to fraud.